Control of hydrocarbon deasphalting process

Abstract

Maximum removal of asphaltic material, including high molecular weight metallic contaminants, from a hydrocarbonaceous charge stock is achieved through the utilization of a solvent extraction zone provided with direct top-heating facilities in the upper portion thereof. The top-heating section of the extraction zone is divided into two liquid-collecting zones in partial open communication with each other. A portion of the liquid is removed from the lower liquid-collecting zone, increased in temperature and returned to the extractor in the upper liquid-collecting zone. The flow rate of liquid withdrawn from the lower zone is controlled in response to the differential pressure between the two liquid-collecting zones.

We claim as our invention: 
     
       1. A process for deasphalting an asphalt-containing hydrocarbonaceous charge stock, in a solvent extraction zone, which comprises the steps of: a. countercurrently contacting said charge stock, introduced into said extraction zone through a first locus thereof, with a hydrocarbon-selective solvent, introduced into said zone through a lower second locus thereof, at extraction conditions selected to produce a solvent-lean asphaltic stream and a solvent-rich hydrocarbon stream;   b. withdrawing said asphaltic stream from said extraction zone through a third locus thereof, said third locus being below said second locus, and a solvent-rich deasphalted oil stream from an upper fourth locus thereof;   c. withdrawing at least a portion of said solvent-rich hydrocarbon stream through a fifth locus intermediate said first and fourth loci, sid fifth locus being in open communication with a lower liquid-collecting zone within a divided top-heating section of said extraction zone;   d. increasing the temperature of said portion of the solvent-rich hydrocarbon stream and introducing the heated portion into said extraction zone through a sixth locus intermediate said fourth and fifth loci, said sixth locus being in open communication with an upper liquid-collecting zone within said divided top-heating section;   e. determining the pressure differential between said lower and upper liquid-collecting zones; and,   f. adjusting the rate at which said solvent-rich hydrocarbon stream is withdrawn through said fifth locus in response to said differential pressure.   
     
     
       2. The process of claim 1 further characterized in that said first and second liquid-collecting zones are in partial open communication with each other. 
     
     
       3. The process of claim 1 further characterized in that said extraction conditions include temperatures in the range of about 50°F. to about 600°F., pressures from about 100 to about 1,000 psig. and a solvent/charge stock volumetric ratio in the range of about 2.0:1.0 to about 30.0:1.0. 
     
     
       4. The process of claim 1 further characterized in that the temperature of the solvent-rich hydrocarbon stream, withdrawn through said fifth locus, is increased about 25°F. to about 125°F. 
     
     
       5. The process of claim 1 further characterized in that the heated solvent-rich hydrocarbon stream is introduced through said sixth locus in a downwardly direction. 
     
     
       6. The process of claim 1 further characterized in that said solvent comprises a light hydrocarbon having from 3 to about 7 carbon atoms per molecule. 
     
     
       7. The process of claim 1 further characterized in that said solvent is a normally liquid naphtha fraction having an end boiling point below about 200°F. 
     
     
       8. The process of claim 6 further characterized in that said solvent comprises a mixture of normal butane and isopentane. 
     
     
       9. The process of claim 6 further characterized in that said solvent comprises a mixture of propane and normal butane. 
     
     
       10. The process of claim 6 further characterized in that said solvent is isopentane. 
     
     
       11. A method for controlling the heat-input to the top-heating section of a solvent extraction zone in which an asphalt-containing charge stock is countercurrently contacted with a hydrocarbon-selective solvent, at extraction conditions selected to produce a solvent-lean asphaltic stream and a solvent-rich hydrocarbon stream, which method comprises the steps of: a. withdrawing at least a portion of said solvent-rich hydrocarbon stream from a first locus in open communication with a lower liquid-collecting zone within said top-heating section;   b. increasing the temperature of the portion of said solvent-rich hydrocarbon stream and introducing the heated portion through a second locus in open communication with an upper liquid-collecting zone within said top-heating section;   c. determining the pressure differential between said lower and upper liquid-collecting zones;   d. developing a signal representative of said pressure differential; and,   e. adjusting the rate at which said solvent-rich hydrocarbon stream is withdrawn through said first locus in response to said signal.   
     
     
       12. The method of claim 11 further characterized in that said first and second liquid-collecting zones are in partial open communication with each other. 
     
     
       13. The method of claim 11 further characterized in that the temperature of the solvent-rich hydrocarbon stream withdrawn through said first locus is increased from 25°F. to about 125°F.